AMD Custom APU 0405 support (Steam Deck GPU)

The Steam Deck’s APU checks all the boxes when it comes to being supported in Blender

That is true according to this:

AMD

GCN 1st gen and newer. Since Blender 2.91, Terascale 2 architecture is fully deprecated, try using Blender 2.90 (albeit not supported, it might still work). List of all AMD GPUs .

Srouce: Requirements — blender.org

But being supported by Blender and being supported by Cycles for GPU rendering are two different things, hence the documentation says it on the same page as above:

These requirements are for basic Blender operation, Cycles rendering using the GPU has higher requirements .

Srouce: Requirements — blender.org

So if we look at what is required for GPU rendering and what the Steam Deck APU is:

HIP is supported on Windows and Linux and requires a AMD graphics card with the Vega architecture or newer. Both discrete GPUs and APUs are supported.

Srouce: GPU Rendering — Blender Manual

Aerith ( Steam Deck ) | Architecture: RDNA 2 | OpenGL: 4.6

Source: List of AMD graphics processing units - Console GPUs - Wikiwand

the "Vega" 7nm instruction set architecture [is] also referred to as Graphics Core Next 5.1.

Source: Graphics Core Next - Wikiwand

That being said, Blender 4.0 got released yesterday, and we can see that:

The minimum required OpenGL version has been increased to 4.3 for Linux and Windows. ( 3478093183 )

Source: Reference/Release Notes/4.0 - Blender Developer Wiki

Support for rendering with AMD RDNA2 and RDNA3 APUs is added.

Source: Reference/Release Notes/4.0/Cycles - Blender Developer Wiki

So maybe it would work on Blender 4.0, with the right drivers.